Aircraft Operations. Volume II - Construction of Visual and Instrument ...

Appendix C to Chapter 1
DETERMINING ILS GLIDE PATH DESCENT/MLS ELEVATION
HEIGHTS AND DISTANCES
1. ILS/MLS glide path heights (H) and horizontal distances (D) from the threshold are calculated by solving a
right-angle triangle:
SI units
where: H = height in metres
Non-SI units
h = reference datum height in metres
D = distance from the threshold in kilometres
θ =glidepathangleindegrees
where: H = height in feet
h = reference datum height in feet
H=h+1000Dtanθ and D = 0.001(H – h) cot θ
H=h+6076Dtanθ and D = 0.0001646(H – h) cot θ
D = distance from the threshold in nautical miles
θ =glidepathangleindegrees
2. The influence of the curvature of the earth’s surface should be considered in order to check that the heights and
distances to the threshold determined in this manner meet the Annex 10 and PANS-OPS requirements. To perform such
a check, Tables II-1-1-App C-1 and II-1-1-App C-2 may be used. For intermediate distances, heights and glide path
angles, the linear interpolation method is used.
For reference datum heights (h) other than 15 m (49 ft):
a) the values obtained from Table II-1-1-App C-1 should be corrected by adding ΔH where:
SI units: ΔH = h – 15 (Table II-1-1-App C-1a))
and
Non-SI units: ΔH = h – 49 (Table II-1-1-App C-1b))
II-1-1-App C-1 23/11/06